1. Field of the Invention
This invention relates to a leakage flux canceling device suitable for use with a cathode-ray tube used in television receiving sets or monitors for various OA equipment.
2. Description of the Related Art
A cathode-ray tube (CRT) used in a television receiving set or a monitor for OA equipment is provided with a canceling device for canceling the leakage flux attributable to a horizontal deflection magnetic field, in order that the horizontal deflection magnetic field leaking out to the front face of the panel may not exceed a prescribed level. FIG. 7 shows an example of a conventional device.
As shown in the figure, a deflecting apparatus 10 has a bell-shaped coil bobbin 12 produced by plastic molding, and horizontal coils (i.e., horizontal deflection coils) 16 are fitted in respective grooves (not shown) formed at predetermined locations on the inner surface of the bell-shaped coil bobbin 12.
The horizontal coils 16 to be used may each be obtained by winding wire with the use of a coil winder (not shown) so that the winding may have a predetermined coil distribution, and then pressing the winding. FIG. 7 exemplifies such coils, wherein the pressed horizontal coils 16 are securely attached to respective predetermined positions of the aforementioned bell-shaped coil bobbin 12.
A ferrite core 13, which is in the form of a truncated cone, is fitted on the outer surface of the bell-shaped coil bobbin 12, and vertical deflection coils (not shown) are fitted around the ferrite core 13. A neck insertion cylinder 17 is formed on one side of the bell-shaped coil bobbin 12 corresponding in position to the neck of a CRT, and a box-shaped cover 20 is attached to the outer surface of the neck insertion cylinder 17. The cover 20 is provided for covering an adjusting ring for a quadrupole magnet, terminals of various lead wires necessary for the deflecting apparatus, and so forth.
A leakage flux canceling device 30 mentioned above is arranged at a front bend (funnel side) of the bell-shaped coil bobbin 12. In the illustrated example, canceling coils 34, which form part of a ring-like body 32, are arranged at substantially symmetrical locations. For the canceling coils 34, automatically wound coils are used.
The ring-like body 32 is attached to the front bend side of the bell-shaped coil bobbin 12 in such a manner that the canceling coils 34 are directed toward the rear bend (neck side). The mounting positions and energization polarities of the pair of canceling coils 34 are selected so that the magnetic flux produced by energization of the canceling coils 34 can cancel the magnetic flux leaking out toward the front face of the panel due to the aforementioned horizontal deflection magnetic field. By providing the canceling device 30, it is possible to greatly reduce the leakage flux to the front face of the panel.
The canceling device 30 described above generally has a structure shown in FIGS. 8 and 9. As shown in the figures, the ring-like body 32 has a groove perpendicular to its circumferential direction (in practice, defined by a pair of flanges 39a and 39b), and guide pieces 36 for mounting canceling coils are formed across portions of the groove at locations almost opposite each other. To obtain the canceling coils 34 as illustrated, wire is wound into square-shape by using a coil winder (not shown) and then the winding is pressed.
The pressed canceling coils 34 are each inserted between a corresponding pair of guide pieces 36 and a U-shaped cover 38 is fitted over each coil 34, whereby the canceling device 30 as shown in FIG. 7 is obtained.
Thus, conventionally the canceling coils 34 are individually formed using a coil winder and capped with the cover 38, and this entails drawbacks such as an increased number of parts, decreased productivity and high cost.
These drawbacks may be eliminated by employing the structure shown in FIG. 10. In the illustrated example, a ring-like body 32 and bobbins 40 and 60 are formed as a one-piece body, and canceling coils 34 are wound on respective flanges formed on the bobbins 40 and 60. With this arrangement, the number of parts is reduced and no covers are required, whereby the decreased productivity is improved and the cost can be cut down.
In the case where the bobbins 40 and 60 are formed integrally with the ring-like body as shown in FIG. 10, however, since the bobbins are each in the form of a rectangular parallelepiped, the space factor is low, and also the bobbins can be caught on an object and damaged during or after the coil winding or during transportation.